The present invention relates, in general, to semiconductor wafer handling, and more particularly, to an apparatus and method for handling very thin and fragile semiconductor wafers.
An array of semiconductor wafer handling equipment is available and works quite well for a large number of semiconductor processing needs. Increasing circuit density increases heat generated by the circuit. To remove this heat from integrated circuits manufacturers use thinner and thinner semiconductor wafers. These thinner wafers break easily, and thus demand more from semiconductor wafer handling equipment. This problem is more acute in the case of compound semiconductors, particularly gallium arsenide (GaAs) which is a factor of two and a half times as brittle as silicon.
Because devices manufactured on GaAs wafers typically operate at high frequencies, flatness and thickness uniformity become more important determinants of electrical performance than is true in silicon devices. Much of the special equipment needed for handling thinned GaAs wafers never had to be developed for silicon manufacturing. Handling of thinned GaAs wafers currently involves a large amount of manual handling, including moving the wafers by sliding them from one flat surface to another. Moreover, manual handling requires special skill and still results in unacceptable damage to the wafers.
Semiconductor wafers can be adhesively mounted on a submount or "handle" which provides a rigid platform to support the fragile wafer and allow automated handling. One problem with submounting, however, is that the wafer must at some point be removed from the submount. In the past, waxes have been used as an adhesive. These waxes had to have a low melting temperature, however, to allow the wax to be melted to remove the wafer from the submount, and to ensure that the wax could be cleaned from the wafer surface. An example of such a process is described in an article entitled "The Direct Demount of Thinned GaAs Wafers to Sawing Tape" by William C. Howell, published in the Proceedings of the Conference on Gallium Arsenide MANufacturing TECHnology (MANTECH), 1990. One problem with low temperature waxes is that they break down, melt, or dissolve during conventional wafer processing such as grinding the back side of the wafers. Alternatively, adhesive tape is used to mount the wafers to the submount. Adhesive tape, however, is difficult to work with, relatively expensive, can distort the shape of the thinned wafer, and results in an unacceptable number of broken wafers if automated taping equipment is used.
What is needed is an apparatus and method for handling fragile semiconductor devices in an automated fashion with minimal wafer breakage.